With rapid industrial development, there is a significant increase in industrial water consumption, which resulted in lack of water; accordingly, water coolers were gradually replaced by air coolers in refineries and petrochemical plants, and later an air-cooling system has began to be used in power plants. The air-cooling system is divided into a direct air-cooling system and an indirect air-cooling system, the later is also divided into two types, i.e., an indirect air-cooling system having a jet type condenser and an indirect air-cooling system having a surface condenser. Since there needs a heat exchange between the cooling water with steam in the pipe(s) in the surface condenser, a terminal temperature difference exists between the cooling water and condensed water. Moreover, the back pressure of the surface condenser is higher than that of the jet type condenser under the same conditions. As a result, the direct air-cooling system and the indirect air-cooling system having jet type condenser may be a trend for the air-cooling system in power stations.
In 1970s and 1980s, large diameter exhaust pipes and a huge vacuum were the bottleneck in the development of the direct air-cooling system. A stand-alone capacity was limited to 200 MW. The direct air cooling system got a rapid development by the end of last century, and the stand-alone capacity was up to 686 MW. In this century a single unit with capacity of 1000 MW has been put into operation. On the other hand, the indirect air-cooling system having jet-type condenser was stayed the way it was in 1970s and 1980s. Until this year, a first set of 600 MW unit of this type was put into operation in the Second Power Plant in Baoji, China. The nozzle arrangement of jet type condenser should be one of the reasons to slow down the development of the indirect air-cooling system. FIG. 1 shows a structure of a single-layered inner water chamber in an existing jet type condenser. Multiple rows of nozzles 1 are arranged at the side of the inner water chamber 2. A water guiding tube 16 in communication with an air-cooling area 6 is provided at the bottom of the inner water chamber 2. The nozzles 1 in the jet type condenser are film nozzles 1 with a jet pressure head of 0.005-0.0225 MPa at which a stable water film can be formed. The jet type condenser in large or medium-sized units with a capacity of over 200 MW is relatively large. The height difference between the nozzle 1 at the top row and the one 1 at the bottom row is more than 800 mm, which makes the water pressure difference therebetween reaches over 0.008 MPa, even though the injection drop (pressure difference during spraying) of design conditions is at a range of 0.005-0.0225 MPa. Since the water-cooling system of the jet type condenser is designed in accordance with the design conditions, when in winter, the desired cooling water flow can be smaller than that required in the design conditions due to the lower temperature of the cooling water. However, the decrease in the amount of cooling water into the jet type condenser will make the water pressure in the inner water chamber 2 below the design conditions. In this case, if spraying film directly, the injection drop of the nozzles 1 at a few rows above may be less than 0.005 MPa, resulted in a poor film. For the jet type condenser in large-sized units, it may be a challenge to make arrangement for the nozzles 1 to reduce the cooling water flow in winter.
For example, in a jet type condenser of a single-layered water chamber in a 200 MW unit putted into operation by our company, the pressure difference of the nozzles 1 at each row is at a range of 0.005-0.0225 MPa when the cooling water flow meets the design conditions. However, under winter conditions, if the cooling water flow is about 60% of that in design conditions, the differential pressure of the nozzles 1 at a few rows above may be less than 0.005 MPa, which results in a poor film-forming effect and spray of water. The cooling water cannot be heated to the saturated temperature, which causes a larger undercooling of condensed water, thereby increasing the heat consumption of the unit.
In order to solve the arrangement problem about the nozzle 1 in a large unit, the applicant filed an application for the patent for invention on a jet type condenser with multilayered inner water chambers (Patent No. CN200810148144) in China in 2008, which has been reviewed and approved by the State Intellectual Property Office of China and the patent was granted in the year of 2010. As shown in FIG. 2, the structure of the inner water chamber in this jet type condenser is a multilayer arrangement along the height direction, comprising an upper inner water chamber 3 and a lower inner water chamber 4, wherein the lower inner water chamber 4 is in communication with an air-cooling area 6 through a water guiding tube 16 at the bottom thereof, and two—four rows of film type nozzles 1 are provided at both sides of the upper inner water chamber 3 and the lower inner water chamber 4. Generally, three rows of nozzles 1-4, 1-5 and 1-6 are provided at the sides of the upper water chamber 3, and three rows of nozzles 1-1, 1-2 and 1-3 are provided at the sides of the lower inner water chamber 4. According to the design specification of the jet type condenser, the cooling water flow entered into the air-cooling area 6 is usually controlled by passage section of the water guiding tube 16 and the water pressure in the lower inner water chamber 4 during the design conditions. In general, the cooling water flow into the air-cooling area 6 is 5% of the total cooling water flow into the condenser under the design conditions.
A cooling water system of the jet type condenser in the Patent No. CN200810148144 is shown in FIG. 3, wherein an upper outer water chamber 9 and a lower outer water chamber 10 are disposed outside the upper inner water chamber 3 and lower inner water chamber 4 respectively. A hot well, provided at the bottom of the shell 8 of the condenser, is in communication with a circulating water output pipeline N on which water pumps 19 are arranged. The other end of the circulating water output pipeline N is in communication with a cooling tower. Through the water pumps 19, some circulating water collected in the condenser shell may be pumped into the cooling tower for cooling. At the same time, the cooling water is delivered by the cooling tower to the upper inner water chamber 3 and the lower inner water chamber 4 through two branch pipes of a cooling water input pipeline M. Valves 17 and 18 are provided at the two branch pipes respectively.
The jet type condenser with multilayered inner water chambers and the cooling water system thereof disclosed in the Patent No. CN200810148144 are applicable for large and medium sized air-cooling units. The condenser with this structure makes the jet pressure of the nozzles 1 at each row basically meet the requirements for jetting an optimal water film, and the film-forming effect of the nozzles 1 of the jet-type condenser having multilayered inner water chambers introduced in this patent has been greatly improved in design conditions.
However, under winter conditions, the required cooling water flow in the condenser is reduced, in this case, the valves 17 and 18 are needed to be adjusted to control the water flow entered into the upper inner water chamber 3 and the lower inner water chamber 4, thereby controlling the water pressure therein. There are two methods to ensure the film-forming effect of the nozzles 1: (1) close the valve 17 and open the valve 18, so that the cooling water can only enter into the lower inner water chamber 4 instead of the upper inner water chamber 3, thus the water pressure in the lower inner water chamber 4 can be maintained to generate a good film formed by the nozzles 1-1, 1-2 and 1-3 at both sides of the lower inner water chamber 4; (2) close the valve 18 and open the valve 17, so that the cooling water can only enter into the upper inner water chamber 3 instead of the lower inner water chamber 4, thus the water pressure in the upper inner water chamber 3 can be maintained to generate a good film formed by the nozzles 1-4, 1-5 and 1-6 at both sides of the upper inner water chamber 3. But there are shortcomings in the two methods. As to the method (1), only the lower inner water chamber 4 is used for spraying film, and the cooling water flow entering into the air-cooling area 6 depends on the passage section of the water guiding tube 16 and the water pressure in the lower inner water chamber 4. The size of the passage section of the water guiding tube 16 is designed in the case that both the upper inner water chamber 3 and the lower inner water chamber 4 are operated together under the design conditions, so that the cooling water flow entering into the air-cooling area 6 can be designed as 5% of the total cooling water flow entering into the condenser. But, only the lower inner water chamber 4 is used in winter, as the passage section of the water conduit 16 is settled, the cooling water flow entering into the air-cooling area 6 may be far greater than 5% of the total cooling water flow entering into the condenser when the water pressure in the lower inner water chamber 4 meets the requirement for the film forming effect of the nozzles 1. In this case, a large amount of cooling water enters into the air-cooling area 6; it's clearly that such cooling water can't be fully heated to a saturated water, thus affecting the performance of the condenser. As to the method (2), only the upper inner water chamber 3 is used for spraying film. In this case, no cooling water enters into the lower inner water chamber 4, and no cooling water enters into the air-cooling area 6, so the steam in the air-cooling area 6 can't obtain a further condensation, which increases the load of the air extracting pump and leads to rising the pressure of the condenser, thus affecting the performance of the turbine. Accordingly, the way to adjust the cooling water system is to keep the valves 17 and 18 to be normally opened, and the pressure in the upper inner water chamber 3 and the lower inner water chamber 4 can be controlled by adjusting the valves 17 and 18. Since the total water flow reduces, the pressure in the upper inner water chamber 3 and the lower inner water chamber 4 is below the design conditions, the film-forming effect of the nozzles at each water chamber gets worse, even the film can't be formed. Thus, the pressure of the upper inner water chamber 3 and the lower inner water chamber 4 can't be improved by such adjustment to guarantee a condensation effect in the condenser under winter conditions, despite of the superficial design of the multilayered inner water chamber.